As a Canadian, I'm going to say I'm not so sure.
The logic people apply in the belief that Japan is going to win is just completely nutzo. It either amounts to "Mecha anime is a thing, so clearly Japan is going to win." or "I think the Kuratas looks cooler so Japan is going to win."
Or just general "Glorious Nippon steel. Cut through tank. Muh animes."
I figure that rationale is going to flop as hard as every Weeaboo's "I am going to move to Japan and become a famous manga writer!" fantasy when they move to Japan and learn that they don't put foreigners on pedestals because they like their cartoons.
Maybe Japan will win. Maybe not. My own speculation? Based solely upon appearances and layman knowledge:
I think America needs a fast K.O. and Japan needs a stamina game.
Kuratas looks a bit more stable, though I'd say the Mrk II looks like it packs a heavier punch.
If the Mrk II starts hammering it really hard right out of the gates and doesn't let up, I think they've got it in the bag.
If Japan can wear them down and then hit them hard later in the game, I think it's their game.
TL:DR I don't think it is an easy fight to call. Both bots have strengths and weaknesses going for them and, imo, weeaboos and 'Muricans are refusing to see that.
That being said - I don't care who wins. My own attitude is similar to the MegaBots one. (Look into their company history/values. For all the bluster, I don't think they would mind loosing as long as it was the advent of giant robot fights as a sport.
I think the only way they will be dissapointed if it is a one time thing. Suidobashi goes back to selling Kuratas to rich nerds and using them as propts in Sci-Fi shows.
Me? I want two things.
An epic god damned fight. For all the bluster of "Lol. I bet America/Japan is going to win in two seconds" from fans. From what I know of the two companies and the brains behind them, I think we are going to get that.
For giant robot fights to become a legitimate sport. Whoever wins and looses, I'll only be sad if this is a one off fight and giant robot fights fade into the ether once it's done.